SENSATION OF LIGHT. 61 acute, or voluminous, according as the source is a dazzling point, or a moderate and wide-spread illumination. The Speciality of the pleasure is the endurability without fatigue, in which respect, sight ranks highest of all the senses, and the same cause renders it the most intellectual. The influence, although powerful for pleasure, is yet so gentle, that it can be sustained in presence and recalled in absence to a distinguishing degree. Whence, as a procuring cause of human and animal pleasure, light occupies a high position; there being a corresponding misery in privation. The intense pleasure of the first exposure after confinement can last only a short time; but the influence, in a modified degree, remains much longer. After excess, a peculiar depression is felt, accompanied with morbid wakefulness and craving for shade. One of the cruellest of tortures was the barbarian device of cutting off the eye-lids, and exposing the eyes to the glare of the sun. As regards Volition, the pleasures of light observe the general rule of prompting us to act for their continuance and. increase. But this does not express the whole fact. There is a well-known fascination in the glare of light, a power to detain the gaze of the eye even after the point of pleasure has been passed. We have here a disturbance of the proper function of the will, of which there are other examples, to be afterwards pointed out. The Intellectual property of the sensations of sight has been already adduced as their speciality. They admit of being discriminated and remembered to a degree beyond any other sense, being approached only by hearing. It is possible that a well-endowed ear may be more discriminative and tenacious of sounds, than a feebly-endowed eye of sights, but, by the general consent, sight is placed above hearing in regard to intellectual attributes. By the Law of Relativity, the pleasures of light demand remission and alternation; hence the art of distributing light and shade. The quantity received, on the whole, may be too much, as in sunny climates, or too little, as in the regions of prevailing fogs. Colour. This is an additional effect of light, serving to extend the optical pleasures, as well as the knowledge, of mankind. The pure white ray is decomposable into certain primary colours, and the presentation of these separately and successively, in the proportions that constitute the solar beam, imparts a new pleasurable excitement, having all the attri hutes of the pleasure of mere light. There is no absolute beauty in any single colour; when we give a preference to red, or blue, or yellow, it is owing to a deficiency as regards that colour, in the general scene. As a rule, the balance of colour, in our experience, is usually in favour of the blue end of the spectrum, and hence red, and its compounds, are a refreshing alternation. Lustre. Some surfaces are said to have lustre, glitter, or brilliancy. This is a complex effect of light. A colour seen through a transparent covering is lustrous, as the pebbles in a clear rivulet. There is also a lustrous effect in a jet black surface, if it reflects the light. This luminous reflection, superadded to the proper visibility of the surface, is the cause of lustre. Transparent surfaces reflect light, like a mirror, as well as transmit the colour beneath; and this multiplication of luminous effects adds to the pleasure. The many-sided sparkle of the cut crystal, or gem, is a favourite mode of giving brilliancy; the broken glitter is more agreeable than a continuous sheet of illumination. The highest beauty of visible objects is obtained by lustre. The precious gems are recommended by it. The finer woods yield it by polish and varnish. The painter's colours are naturally dead, and he superadds the transparent film. This property redeems the privation of colour, as in the lustrous black. The green leaf is often adorned by it, through the addition of moisture. Possibly much of the refreshing influence of greenness in vegetation is due to lustrous greenness. Animal tissues present the effect in a high degree. Ivory, mother of pearl, bone, silk, and wool, are of the class of brilliant or glittering substances. The human skin is a combination of richness of colouring with lustre. The hair is beautiful in a great measure from its brilliancy. The finest example is the eye; the deep black of the choroid, and the colours of the iris, are liquified by the transparency of the humours. 6. The sensations involving the Muscular Movements of the eye are visible movement, visible form, apparent size, distance, volume, and situation. Visible Movement. The least complicated example of the muscular feelings of sight is the following a moving object, as a light carried across a room. The eye rotates, as the light moves, and the mental effect is a complex sensation of light and movement. If the flame moves to the right, the right muscles contract; if to the left, the left muscles; and so on; there being different muscles, or combinations of muscles, engaged VISIBLE MOVEMENT. 63 for every different direction. Instead of following a straight course, the light may change its direction to a bend or a curve. This varies the muscular combinations, and their relative pace of contraction; whence results a distinguishable mode of consciousness. Thus it is, that one and the same optical effect, as a candleflame or a spark, may be imbedded in a great variety of muscular effects, every one of which is distinguished from the rest, and characteristically remembered. The embodiment must be contained in the numerous nerve centres and nerve communications related to the muscles of the eye. As with the muscles generally, we can distinguish, by the muscles of the eye, longer or shorter continuance of movement. We can thus estimate, in the first place, duration; and, in the second (under certain conditions), visual or apparent extension. In like manner, we are conscious of degrees of speed or velocity of movement, which also serves as an indirect measure of visible extension. The kind of muscular sensibility that, from the nature of the case, cannot belong to the eye, is the feeling of Resistance or dead strain, there being nothing to constitute a resisting obstacle to the rotation of the ball, except its own very small inertia. Hence the eye, with all its wide-ranging and close-searching capabilities, cannot be said to contribute to the fundamental consciousness of the object universe, the feeling of resistance. . The various pleasures of movement, formerly recited, appertain to moving spectacle. The massive, languid feeling of slow movements, the excitement of a rapid pace, the pleasures of waxing and waning movements (the beauty of the curve), can be realized through vision. Among the permanent imagery of the intellect, recalled, combined, and finally dwelt upon, we are to include visible. movements. The familiar motions of natural objects-running streams, waving boughs, &c.; the characteristic movements of animals, the movements and gestures of human beings, the moving machinery and processes of industry-are distinguished and remembered by us, and form part of our intellectual furniture. Visible Form. This supposes objects in stillness, surveyed in outline by the eye, and introduces us to co-existence in Space, as contrasted with succession in Time. With regard to the mere fact of muscular movement, it is the same thing for the eye to trace the outline of the rainbow, as to follow the flight of a bird, or a rocket. But, as in the case of Touch, already considered, the accessary circumstances make a radical difference, and amount to the contrast of succession with co-existence. The points of distinction are these:—(1) In following the outline of the rainbow, we are not constrained to any one pace of movement, as with a bird, or a projectile. (2) The optical impression is not one, but a series, which may be a repetition of the same, as the rainbow, or different as the landscape. (3) We may repeat the movement, and find the same series, in the same order. (4) We can, by an inverted movement, obtain the series in an inverted order. These two experiences-repetition and inversion-stamp a peculiar character of fixity of expectation, which belongs to our idea of the extended and co-existing in space, as opposed to passing movement. (5) As regards sight in particular when compared with touch, the power of the eye to embrace at one glance a wide prospect, although minutely perceiving only a small portion, confirms the same broad distinction, between the starry sky and the transitory flight of a meteor. When a series of sensations can be simultaneously grasped, although with unequal distinctness, this gives, in a peculiar manner, the notion of plurality of existence, as opposed to continued single existence. The course moved over by the eye in scanning an outline, leaves a characteristic muscular trace, corresponding to the visible form. Thus we have Linear forms-straight, crooked, curved, in all varieties of curvature; Superficial forms and outlines-round, square, oval, &c. The visible objects of the world are thus distinguished, identified and retained in the mind as experiences of optical sensation embedded in ocular movements; and we have a class of related feelings, pleasureable and otherwise, the same as with visible movements. Our intellectual stores comprise a great multitude of visible forms. Apparent Size. The apparent size or visible magnitude embraces two facts, an optical and a muscular. The optical fact is the extent of the retina covered by the image, called by Wheatstone the retinal magnitude; the muscular fact is the muscular sweep of the eye requisite to compass it. These two estimates coincide; they are both reducible to angular extent, or the proportion of the surface to an entire sphere. The apparent diameter of the sun, and of the full moon, is half a degree, or of the circumference of the circle of the sky. This combined estimate, by means of two very sensitive organs the retina and the ocular muscles, renders our estimate of apparent size remarkably delicate; being, in fact, the VISIBLE MAGNITUDE.-DISTANCE. 65 universal basis of all accurate estimate of quantity. In measuring other properties of bodies, as real magnitude, weight, heat, &c., we reduce each case to a comparison of two visible magnitudes; such are the tests of a three-foot rule, a balance, a thermometer. The fluctuations of apparent size in the same thing-a remote building for example-are appreciated with corresponding delicacy; and when we come to know that these fluctuations are caused by change of real distance, we use them as our most delicate indication of degrees of remoteness. The celestial bodies are conceived by us solely under their apparent or visible size. Terrestrial objects all vary in visible size, and are pictured by the mind under a more or less perfect estimate of real size. Distance, or varying remoteness. We have as yet supposed visible movement and form in only two dimensions, or as extending horizontally and vertically. The circumstance of varying remoteness, necessary to volume, or three dimensions, demands a separate handling. We must leave out, at this stage, the knowledge of real distance, as well as real magnitude. is accom There are two adaptations, or adjustments, of the eyes for distance; a change in the ball for near distances, and a convergence or divergence of the two eyes for a wider range. Both changes are muscular; they are accompanied with a consciousness of activity, or the contraction of muscles. The change made, in each eye-ball, for a nearer distance is a conscious change; the return from that is also conscious. The gradual convergence or divergence of the two eyes panied with a discriminative muscular consciousness. We can thus, by muscularity, discriminate (although not as yet knowing the whole meaning of) bodies moving away from the eye, or approaching nearer it. An object moving across the field of view is distinguished from the same object retreating or advancing; distinct muscles being brought into play. may, likewise, have the emotional effects of slow, quick, or waning movements, by change of distance from the eye. As a general rule, there is a relief in passing from a near view to a distant. We We have seen, under the previous head, that variation of optical size accompanies variation of distance, and is the most delicate test of all. To this we have to add the binocular dissimilarity, which is at the maximum for near distances, and is nothing for great remoteness. There are thus four separate circumstances engaged in making us aware of any alteration |